13.6 cf ported sub box

ok i got a pair of boxes i built downstairs .. thier too heavy to move but the construction is solid 3/4 inch MDF.. i installed the best 18 inch sub into it that i could get from Pyramid. I like pyramid alot , thier products have served me well over the years.
anyway i was told by a few members on here that its really running at 19 HZ cuz it is 13.6 cubic feet (4 feet tall 2 feet wide 2 feet deep) and it got a 4 inch diameter port tube thats 4 inches deep.
so that being the case... if i want to create a broader range of bass.. like higher frequencies n whatnot.. should i get a longer port tube?? and if so ... how long?? i just want to make it so it will have a range of 35Hz down to maybe 19 Hz or somethin . that is all i want to do.. i had NO idea this would be complicated lol please let me know about the port. cuz i mite have to use some PVC piping which is kool with me cuz im all about the bass. not looks

Re: 13.6 cf ported sub box

i sell and represent pyramid, it is a reputable company. there is nothing wrong with thier products that is why i USE them personally as well as selling them. i never had problems.
but i would appreciate if people would focus on the thread topic and the problem i have with the box and not criticize my choice in speakers.
thank you